1、DRAFT FOR DEVELOPMENT DD ENV 13070:1998 Fruit and vegetable juices Determination of the stable carbon isotope ratio ( 13 C/ 12 C) in the pulp of fruit juices Method using isotope ratio mass spectrometry ICS 67.160.20DDENV 13070:1998 This Draft for Development, having been prepared under thedirection
2、 of the Consumer Products and Services Sector Board, was published under theauthority of the Standards Boardand comes into effect on 15July1998 BSI 04-1998 ISBN 0 580 29879 5 National foreword This Draft for Development is the English language version of ENV13070:1998. This publication is not to be
3、regarded as a British Standard. It is being issued in the Draft for Development series of publications and is of a provisional nature. It should be applied on this provisional basis, so that information and experience of its practical application may be obtained. Comments arising from the use of thi
4、s Draft for Development are requested so that UK experience can be reported to the European organization responsible for its conversion into a European Standard. A review of this publication will be initiated 2 years after its publication by the European organization so that a decision can be taken
5、on its status at the end of its three-year life. The commencement of the review period will be notified by an announcement in Update Standards. According to the replies received by the end of the review period, the responsible BSI Committee will decide whether to support the conversion into a Europe
6、an Standard, to extend the life of the prestandard or to withdraw it. Comments should be sent in writing to the Secretary of BSI Technical Committee AW/21, Fruit and vegetable juices, at389 Chiswick High Road, London W4 4AL, giving the document reference and clause number and proposing, where possib
7、le, an appropriate revision of the text. A list of organizations represented on this committee can be obtained on request to its secretary. Cross-references The British Standards which implement international or European publications referred to in this document may be found in the BSI Standards Cat
8、alogue under the section entitled “International Standards Correspondence Index”, or by using the “Find” facility of the BSI Standards Electronic Catalogue. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, theENV title page, pages 2 to 7 and a back cover
9、. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover. Amendments issued since publication Amd. No. Date CommentsDDENV13070:1998 BSI 04-1999 i Contents Page National foreword Inside fron
10、t cover Foreword 2 Text of ENV 13070 3ii blankEUROPEAN PRESTANDARD PRNORME EUROPENNE EUROPISCHE VORNORM ENV 13070 May 1998 ICS 67.160.20 Descriptors: Fruit and vegetable juices, pulps, chemical analysis, determination, ratios, isotopes, carbon, mass spectrometry English version Fruit and vegetable j
11、uices Determination of the stable carbon isotope ratio ( 13 C/ 12 C) in the pulp of fruit juices Method using isotope ratio mass spectrometry Jus de fruits et de lgumes Dtermination du rapport des isotopes stables du carbone ( 13 C/ 12 C) dans la pulpe des jus de fruits Mthode utilisant la spectromt
12、rie de masse des rapports isotopiques Frucht- und Gemsesfte Bestimmung des Verhltnisses der stabilen Kohlenstoff-Isotope ( 13 C/ 12 C) in der Pulpe von Fruchtsften Verfahren unter Anwendung der Isotopenverhltnis-Massenspektroskopie This European Prestandard (ENV) was approved by CEN on 9April1998 as
13、 a prospective standard for provisional application. The period of validity of this ENV is limited initially to three years. After two years the members of CEN will be requested to submit their comments, particularly on the question whether the ENV can be converted into a European Standard. CEN memb
14、ers are required to announce the existence of this ENV in the same way as for an EN and to make the ENV available promptly at national level in an appropriate form. It is permissible to keep conflicting national standards in force (in parallel to the ENV) until the final decision about the possible
15、conversion of the ENV into an EN is reached. CEN members are the national standards bodies of Austria, Belgium, CzechRepublic, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom. CEN European Co
16、mmittee for Standardization Comit Europen de Normalisation Europisches Komitee fr Normung Central Secretariat: rue de Stassart 36, B-1050 Brussels 1998 CEN All rights of exploitation in any form and by any means reserved worldwide for CEN national Members. Ref. No. ENV 13070:1998 EENV 13070:1998 2 B
17、SI 04-1999 Foreword This European Prestandard has been prepared by Technical Committee CEN/TC 174 “Fruit and vegetable juices Methods of analysis”, the secretariat of which is held by AFNOR According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following count
18、ries are bound to announce this European Prestandard: Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and the UnitedKingdom. Contents Page Foreword 2 1 Scope 3 2 Normative refe
19、rences 3 3 Symbols 3 4 Principle 3 5 Reagents 3 6 Apparatus 3 7 Procedure 4 8 Calculation 5 9 Precision 5 10 Test report 6 Annex A (informative) Bibliography 7 Annex B (informative) Statistical results of the interlaboratory test 7 Table B.1 7ENV13070:1998 BSI 04-1999 3 1 Scope This European Prestan
20、dard specifies a method for the determination of the stable carbon isotope ratio of the pulp in fruit juices. The determination of this parameter is useful as an internal standard for comparison with the Carbon13 content value ($ 13 C) obtained for the sugars. 2 Normative references This European Pr
21、estandard incorporates by dated or undated reference, provisions from other publications. These normative references are cited at the appropriate places in the text and the publications are listed hereafter. For dated references, subsequent amendments to or revisions of any of these publications app
22、ly to this European Prestandard only when incorporated in it by amendment or revision. For undated references the latest edition of the publication referred to applies. EN ISO 3696:1995, Water for analytical laboratory use Specification and test methods. ISO 5725:1986, Precision of test methods Dete
23、rmination of repeatability and reproducibility for a standard test method by inter-laboratory tests. ENV 12140:1996, Fruit and vegetable juices Determination of the stable carbon isotope ratio ( 13 C/ 12 C) ofsugars from fruit juices Method using isotope ratio mass spectrometry. 3 Symbols For the pu
24、rpose of this standard the following symbols apply: 4 Principle The carbon contained in the pulp is quantitatively combusted into carbon dioxide. The ratio of the two stable carbon isotopes ( 13 C and 12 C) is then measured using a isotope ratio mass spectrometer. This value can then be compared wit
25、h the value obtained for the sugars (as determined using ENV12140). If there is too large a difference between the value in the pulp and the sugars this can indicate the addition of sugars derived from aC 4plant such as cane or corn. 5 Reagents Use only reagents of recognized analytical grade and on
26、ly water in accordance with at least grade 3 of ENISO3696:1995. 5.1 Calcium hydroxide 5.2 Sulfuric acid, 95% to 97% (m/m) 5.3 Acetone 6 Apparatus Usual laboratory apparatus and, in particular, the following: 6.1 Isotope ratio mass spectrometer, with the ability to determine the 13 C content of CO 2g
27、as at natural abundance with a precision of 0,05% or better expressed as relative $ value (see8) (one measuring cycle with ten integration periods). The mass-spectrometer will generally be fitted with a triple collector to simultaneous register at mass number44, 45 and46. The mass spectrometer shoul
28、d be fitted either with a dual inlet system, for alternately measuring the unknown sample and a standard, or use an on-line system which combusts the sample in an elemental analyser(6.2) followed by gas chromatographic separation of the combustion products prior to isotopic mass spectrometric determ
29、ination. The former method offers the highest accuracy for the determination of variations of the isotope content in the range of the natural abundance. However, correct results can also be obtained using the on-line method provided a secondary standard is used. ( 13 C/ 12 C) Isotope ratio of carbon
30、 13 to 12 for a considered sample; $ 13 C Carbon 13 ( 13 C) content expressed in parts per thousand (); g Acceleration due to gravity at the surface of the earth (9,81 m/s 2 ).ENV 13070:1998 4 BSI 04-1999 6.2 Combustion apparatus (elemental analyser), which can quantitatively converts all the carbon
31、 of the sample into carbon dioxide (CO 2 ), and which is able to convert all nitrous oxides formed, during the oxidation process, into nitrogen gas and to remove all other combustion products, including water, from the CO 2 . 6.3 Centrifuge, capable of producing a centrifugal acceleration of 1 400 g
32、 at the base of the centrifuge tube(6.4). NOTEThe rotational frequency required to give correct centrifugal acceleration can be calculated from the following equation: 6.4 Centrifuge tubes, of 50 ml capacity. 7 Procedure 7.1 Preparation of the test sample 50ml of fruit juice (natural or reconstitute
33、d) is centrifuged at 1 400 g for 10min to separate the uspended solids (pulp). To remove any adhering sugars the centrifugate is washed with water. To achieve this the pellet is resuspended in40ml of water and stirred for 5min. This suspension is then recentrifuged and the water discarded. A fresh a
34、liquot of water is added and the process is repeated. A further aliquot of water is used in the third and final wash with water. After this third wash, with water, the pulp is resuspended in 40ml of acetone to extract any lipid material. After stirring in acetone the pulp is centrifuged as given abo
35、ve and the pulp separated from the solvent. A fresh aliquot of acetone is added and the process repeated twice more. To obtain meaningful results it is essential that both the water and acetone washes are carried thoroughly. This ensures that all the occluded sugars and lipid materials are removed.
36、If the pulp is not properly washed the lipid material will cause a significant negative shift in the $ 13 C content of the pulp. The pulp after washing, as described above, is finally dried under vacuum which gives a white/gray solid which can be easily homogenised. 7.2 Combustion of pulp Combust th
37、e samples obtained using the procedures given in7.1 using the procedure for sugars described in ENV12140:1996. Care should be taken to ensure that there is a quantitative reduction of all the nitrous oxides formed, from the nitrogen containing compounds in the pulp, during the combustion stage. If t
38、his is not achieved nitrous oxide will be present in the carbon dioxide gas and this will contribute to the intensity of the mass46 ion. This will lead to an incorrect correction for oxygen17 and so give a too low carbon13 content of the pulp. NOTESuitable microcombustion systems are commercially av
39、ailable. 7.3 Determination The 13 C/ 12 C isotope ratio in the carbon dioxide obtained from the combustion of the pulp, as described in7.2, is determined with the aid of an isotope ratio mass spectrometer(6.1). Determine the ratio for the isotopic species 13 CO 2 / 12 CO 2from the corresponding inte
40、nsities. a = 11,18 r (n /1 000) 2 (1) where: a is the centrifugal acceleration; r is the radius of the centrifuge in centimetres, measured from the mid point (the centrifuge axis) to the bottom of the centrifuge tube when swung out; n is the rotational frequency per minute.ENV13070:1998 BSI 04-1999
41、5 8 Calculation In addition to the commonly used mass abundance (in of atoms), the so-called delta value ($) is also used as an alternative system of units for indicating isotope content. Delta values are used exclusively for indicating variations (on the third decimal place) in the natural isotopic
42、 abundance. Express the $ 13 C values as the relative difference per thousand between the 13 C and 12 C ratios of a sample in relation to a standard, the Pee Dee Belemnite from South Carolina-USA (the PDB standard). This is a fossil calcium carbonate with an isotope ratio ( 13 C/ 12 C) PDB= 0,011237
43、2 for the emitted CO 2 . This value is the reference point of the common international PDB scale for$ 13 Cvalues expressed in parts per thousand () which are calculated using the following equation: A suitable secondary standard for routine use in this method is NBS22 obtained from International Ato
44、mic Energy Agency (IAEA 1) , Vienna), which has a $ 13 C value of 29,80 relative to PDB. 9 Precision Details of the interlaboratory test on the precision of the method are summarized inAnnex B. The values derived from interlaboratory test may not be applicable to analysis of concentration ranges and
45、 matrices other than those given inAnnex B. 9.1 Repeatability The absolute difference between two single results found on identical test material by one operator using the same apparatus within the shortest feasible time interval will exceed the repeatability limit r in not more than 5% of the cases
46、. The values are: (2) 1) International Atomic Energy Agency P.O. Box 100 A-1400 Wien Austria. orange juice r = 0,32; orange juice with added sugar r = 0,31; grapefruit juice r = 0,26; grapefruit juice with added sugar r = 0,45; pineapple juice r = 0,42; pineapple juice with added sugar r = 0,46;ENV
47、13070:1998 6 BSI 04-1999 9.2 Reproducibility The absolute differences between two single test results on the identical material reported by two laboratories will exceed the reproducibility limit R in not more than 5% of the cases. The values are: 10 Test report The test report must contain the follo
48、wing data: all information necessary for the identification of the sample (kind of sample, origin of sample, designation); a) a reference to this European Standard; b) the date and type of sampling procedure (if known); c) the date of receipt; d) the date of test; e) the test results and units in wh
49、ich they have been expressed; f) any particular points observed in the course of the test; g) any operations not specified in the method or regarded as optional, which might have affected the results. orange juice R = 1,03; orange juice with added sugar R = 0,92; grapefruit juice R = 0,78; grapefruit juice with addedsugar R = 2,35; pineapple juice R = 3,00; pineapple juice with addedsugar R = 2,08;ENV13070:1998 BSI 04-1999 7 Annex A (informative) Bibliography H.Craig, Geochim. Cosmochim. A
